The present invention relates to a press fabric for a pulp machine which is used at pressing parts of the pulp machine and has excellent water-sucking ability, washing ability, showering resistance, and abrasion resistance, particularly a press fabric for the pulp machine suitable for a double wire machine such as heavy-duty press, and, of course, usable in a double wire press forming a pulp sheet having both functions of dewatering and pressing.
Pulp manufacturing method is a well-known technology, wherein a raw material containing pulp fibers etc. is generally conveyed from a head box and fed to an endless fabric for making pulp which runs with being suspended between the rolls of a pulp sheet-manufacturing apparatus. The raw material fed is transferred together with the running of the fabric and moisture is removed by a dehydrating apparatus or the like to form a pulp sheet during the transfer. The pulp sheet formed is then transferred to a press part and, if necessary, to a dryer part. At the press part, the pulp sheet is transferred by a felt for pressing. Moisture is further discharged by passing through a series of press nip constituted by the combination of the felt and press rolls. Alternatively, in a heavy duty press or double wire press, a method of placing a pulp sheet to be a raw material of paper between two felts and sucking water by nip pressure is used. At the dryer part, the pulp sheet is transferred by a canvas and the pulp sheet is finally manufactured by drying.
The water-sucking medium hitherto used at the press part includes felts and woven fabrics. Specifically, examples include a needle felt wherein a batt of a synthetic fiber is crossed by needling on the front and back surface of a base cloth woven with a monofilament or a multifilament, a fabric obtained by weaving by a loom using the warp and weft of a monofilament and making endless by tying up through weaving, and a fabric woven by a hollow weave machine using a multifilament as the upper weft and lower weft and a monofilament as the warp. The fabric woven by a hollow weave loom is formed as an endless one at the stage of weaving by the loom. Since the fabric has a characteristic that the relation between the warp and weft is reversed on the loom and at use, the above fabric woven as hollow weave becomes a fabric of double warp and single weft weave at use.
Since the needle felt has a structure filled with fine batt of synthetic fiber from the front surface to back surface, it is a water-sucking medium having a low water-flow resistance and a good water-sucking ability. When it absorbs water from a pulp sheet, fine fibers, chemicals, etc. simultaneously enter into the felt, and their removal requires vigorous washing. However, the contaminants are difficult to remove owing to the structure filled with fine batt of synthetic fiber, so that the remaining contaminants causes dewatering blotches and the use of high pressure washing shower for washing the contaminants etc. sometimes results in the occurrence of hole formation through the cleavage of the batt fiber by the impact of shower pressure. In addition, since the felt has a bad cushioning property and nipping resistance, there is a problem that the batt is broken and gradually compressed to reduce the thickness during the use, and in proportion thereto, the water-sucking ability decreases.
Moreover, there is a defect that the felt has a bad elongation rigidity, flexure rigidity, stability of size and position. For good running of the felt on which a pulp sheet is loaded, it is necessary to transfer the power of driving rolls surely to the felt in the state that tension is applied. However, the needle felt has a weak elongation rigidity and also exhibits a large shrinkage of width and a large decrease of thickness which occur in proportion to the elongation, so that it is impossible to apply a large tension and thus a good running cannot be effected.
Also, there is a problem of a slip. The occurrence of a slip has resulted problems that the abrasion of the running surface of the felt is accelerated and electrical load is increased to stop the machine, and has sometimes exerted a serious influence on the productivity. In addition, since the felt is weak in flexure rigidity, it cannot resist the weight of a raw material and deflection has sometimes occurred to result in the breaking or crack of the pulp sheet.
Furthermore, with the needle felt, there is a problem that manufacturing cost is high because it takes a lot of trouble and time to carrying out needling, heating after the needling, compaction of the felt by mechanical compaction, and the like. Although the needle felt is a water-sucking medium excellent in water-sucking ability, but has several serious problems in washing ability, rigidity, dimensional stability, etc.
Therefore, other than the needle felt, a single fabric or a double-warp fabric has been employed regarding washing ability and rigidity as important. The single fabric is manufactured by weaving a monofilament having a high high-pressure washing-shower resistance used as the warp and weft, and was made endless by a well-known method of tying up through weaving. However, these fabrics has a bad water-sucking ability owing to the absence of fine fiber spaces effective for water-sucking and also lacks flexibility and cushioning property, so that there arises a problem that a pulp sheet is broken under a high nip pressure, and thus it is extremely difficult to impart the properties required in the press step.
Moreover, the fabric woven and formed as an endless one at the stage of weaving with a hollow weave loom has hitherto been used because of the advantage of saving the trouble of tying up through weaving. In the case of hollow weave, since the relation between the warp and the weft is reversed on the loom and at use, the fabric manufactured by weaving a multifilament weft arranged doubly and a single monofilament warp arranged singly became a fabric of double multifilament warp and single monofilament weft having a structure that the weft is protruded to the running surface side.
The most protuberant monofilament weft to the running surface side is gradually crushed with a high nip pressure by pressing, and as the protrusion of the monofilament weft becomes small, the multifilament of the warp comes into contact with the press rolls. After the fabric reaches this state, the moisture contained in the fabric begins to move effectively to the press rolls and a sufficient water-sucking is effected. Precisely, an excess moisture from the pulp sheet moves to the fabric from the pulp sheet with nip pressure by pressing, passes through fine water-sucking spaces of the multifilament constituting the fabric, and a series of dewatering is completed by bringing the multifilament containing moisture into contact with the rolls. In the case of a structure that a monofilament is the most protuberant and thus a multifilament do not sufficiently come into contact with the press rolls, there are problems that water-sucking ability is bad until the multifilament of the warp is brought into contact with the press rolls, and moreover, the protruded monofilament is severely abraded by friction with the rolls.
As described above, a needle felt or a conventional press fabric manufactured by weaving a monofilament and a multifilament cannot serve excellent effects in water-sucking ability, washing ability, showering resistance, and abrasion resistance.
In view of the problems of the conventional technology, the present invention is to provide a press fabric for a pulp machine excellent in water-sucking ability, washing ability, showering property, and abrasion resistance.
A press fabric for a pulp machine of this invention is a weft-abrading type fabric obtained by weaving a monofilament used as a warp and a bundled yarn as a weft. The bundled weft yarn has fine water-sucking spaces formed by bundling up raw filaments of a small diameter and forms the most protuberant crimp on the surface of the fabric. The most protuberant crimp may particularly be formed on the running side surface of the fabric.
Also, a press fabric for a pulp machine of this invention is a weft-abrading type fabric obtained by weaving in a multi-layer state a monofilament used as a warp and a bundled yarn as a weft. The bundled yarn forms the most protuberant crimp on a surface of the fabric.
More detailed embodiments of this invention will be described below.